In recent years, improving harmony with the global environment and decreasing the environmental burden have become significant goals of the industry and the development of products and technologies has been speeded up out of concern for the environment. There has been a similar movement in the technical field of the present invention, in particular, the regulation of the use of an organotin compound has been strengthened among developed countries, since it has become a problem that the organotin catalyst, which is widely used as a catalyst for a polyurethane resin, is harmful for human bodies due to its high toxicity, environmental hormones, and the like. In the spectacle lens industry which uses this polythiourethane resin, there is a need for the development of a catalyst to replace the organotin catalyst. As for tin-free non-metal catalysts capable of giving common thermocurable resins, an amine compound, an amine carboxylate, phosphine, and the like are known (Patent Documents 1, 2, 3, 4 and 5). In addition, a quaternary ammonium salt compound is known to be used in combination with a carboxylic acid metal compound (Patent Document 6).
Furthermore, to prepare a polythiourethane resin as a material for a plastic lens, a casting polymerization method in which a polymerizable composition is injected into a mold for heat curing is generally employed. In this method, the polymerization reaction is carried out while the temperature is gradually raised from a low temperature to a high temperature over a period of several hours to several tens of hours. At that time, in order to obtain an optically homogeneous plastic lens, it is necessary to add a catalyst to slowly carry out a heat controlled polythiourethanization reaction, thereby preventing the occurrence of thermal inhomogeneity while the temperature is raised. Furthermore, in order to fully realize the physical properties of the resin including its optical properties, heat resistance, and strength, it is necessary to complete the polymerization. In order to complete the polymerization, a method in which a catalyst with strong polymerization activity is used, or a method in which the amount of the catalyst is increased might be considered. However, such methods have problems such as the polymerization reaction progresses until the prepared polymerizable composition is injected into a mold, in other words, sufficient pot life cannot be secured. Furthermore, there is another problem that exothermic heat is locally generated during polymerization and then optical inhomogeneity occurs frequently in the lenses. As a method of solving this problem, there have been reports, for example, of a case in which the low-temperature activity is suppressed using a Lewis acid in combination with a tertiary amine with strong activity (Patent Document 6).
However, if a conventionally known non-metal catalyst is used as a catalyst for polythiourethanization, the catalyst activity in the low-temperature zone is too strong, and runaway polymerization occurs. Thus, such a catalyst is not good enough as the catalyst for producing the optical transparent resin for a plastic lens for spectacles, and the like, since sufficient heat resistance may not be obtained and cloudiness is generated in the obtained resin depending on the resins to be cured.
[Patent Document 1] Japanese Patent Laid-open No. H03-084021
[Patent Document 2] Japanese Patent Laid-open No. S63-077918
[Patent Document 3] Japanese Patent Laid-open No. S62-016484
[Patent Document 4] Japanese Patent Laid-open No. H09-077850
[Patent Document 5] Japanese Patent Laid-open No. 2000-256571
[Patent Document 6] Japanese Patent Laid-open No. 2005-105084